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| -rw-r--r-- | virtio-gpu.tex | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/virtio-gpu.tex b/virtio-gpu.tex index 34cf493..22546cc 100644 --- a/virtio-gpu.tex +++ b/virtio-gpu.tex @@ -34,6 +34,7 @@ control queue. \begin{description} \item[VIRTIO_GPU_F_VIRGL (0)] virgl 3D mode is supported. +\item[VIRTIO_GPU_F_HOST_ALLOC (1)] buffer allocation by the host is supported. \end{description} \subsection{Device configuration layout}\label{sec:Device Types / GPU Device / Device configuration layout} @@ -90,6 +91,11 @@ height and format along with an identifier. The guest must then attach backing store to the resources in order for DMA transfers to work. This is like a GART in a real GPU. +Additionally, when the VIRTIO_GPU_F_HOST_ALLOC feature is present, the guest +can request the host to allocate backing store for resources on its behalf, in +which case the allocated resources can be accessed by both the host and the +guest without any need for DMA transfers. + \subsubsection{Device Operation: Create a framebuffer and configure scanout} \begin{itemize*} @@ -120,6 +126,18 @@ using VIRTIO_GPU_CMD_SET_SCANOUT and VIRTIO_GPU_CMD_RESOURCE_FLUSH, and update the invisible framebuffer using VIRTIO_GPU_CMD_TRANSFER_SEND_2D. +\subsubsection{Device Operation: Create a framebuffer from host-allocated memory} + +\begin{itemize*} +\item Create a host resource using VIRTIO_GPU_CMD_RESOURCE_CREATE_2D. This + step is identical to the guest-allocated backing store case. +\item Request the host to allocate the backing storage for the resource just + created, using VIRTIO_GPU_CMD_RESOURCE_ALLOC_BACKING. The host will map the + memory to the guest and will return the memory address. +\item Use VIRTIO_GPU_CMD_SET_SCANOUT, VIRTIO_GPU_CMD_TRANSFER_SEND_2D and + VIRTIO_GPU_CMD_RESOURCE_FLUSH as for guest-allocated memory. +\end{itemize*} + \subsubsection{Device Operation: Multihead setup} In case two or more displays are present there are different ways to @@ -171,6 +189,7 @@ enum virtio_gpu_ctrl_type { VIRTIO_GPU_CMD_TRANSFER_TO_HOST_2D, VIRTIO_GPU_CMD_RESOURCE_ATTACH_BACKING, VIRTIO_GPU_CMD_RESOURCE_DETACH_BACKING, + VIRTIO_GPU_CMD_RESOURCE_ALLOC_BACKING, /* cursor commands */ VIRTIO_GPU_CMD_UPDATE_CURSOR = 0x0300, @@ -179,6 +198,7 @@ enum virtio_gpu_ctrl_type { /* success responses */ VIRTIO_GPU_RESP_OK_NODATA = 0x1100, VIRTIO_GPU_RESP_OK_DISPLAY_INFO, + VIRTIO_GPU_RESP_OK_ALLOC_BACKING, /* error responses */ VIRTIO_GPU_RESP_ERR_UNSPEC = 0x1200, @@ -417,6 +437,34 @@ struct virtio_gpu_resource_detach_backing { This detaches any backing pages from a resource, to be used in case of guest swapping or object destruction. +\item[VIRTIO_GPU_CMD_RESOURCE_ALLOC_BACKING] Request the host to allocate + backing pages for a resource. Request data is \field{struct + virtio_gpu_resource_alloc_backing}. Response type is + VIRTIO_GPU_RESP_OK_ALLOC_BACKING, response data is \field{struct + virtio_gpu_resp_resource_alloc_backing}. + +\begin{lstlisting} +struct virtio_gpu_resource_alloc_backing { + struct virtio_gpu_ctrl_hdr hdr; + le32 resource_id; + le32 padding; +}; + +struct virtio_gpu_resp_resource_alloc_backing { + struct virtio_gpu_ctrl_hdr hdr; + le64 addr; +}; +\end{lstlisting} + +This allocates backing store memory for a resource on the host, and maps the +memory physically contiguous to the guest. The host returns the guest memory +address in the \field{addr} field. If memory can't be allocated, the response +is VIRTIO_GPU_RESP_ERR_OUT_OF_MEMORY with no data. + +When the backing store is detached from the resource with +VIRTIO_GPU_CMD_RESOURCE_DETACH_BACKING, the memory is freed and unmapped from +the guest. + \end{description} \subsubsection{Device Operation: cursorq}\label{sec:Device Types / GPU Device / Device Operation / Device Operation: cursorq} |